A longitudinal study of risk factors for incipient periodontal disease in adolescents continued in 226 Navajo Indians, aged 14- 18. The second of three rounds of clinical, radiographic and microbiologic data was completed. Analysis of the baseline data indicated that the risk of loss of periodontal attachment is increased by exposure to both B. gingivalis and H. actinomycetencomitans; both associations are confounded by the presence of dental calculus and gingivitis. Therefore, both stratified and multiple logistic regression analyses have been undertaken to remove the effect of confounding.